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						<h1 id="firstHeading" class="firstHeading" lang="en"><span dir="auto">Gamma</span></h1>
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								<div id="siteSub">From PanoTools.org Wiki</div>
								
												
				<div id="mw-content-text" lang="en" dir="ltr" class="mw-content-ltr"><p><br />
<b>Gamma</b> is the relation between pixel value respectively electric power and visible brightness on a specific output medium. 
</p><p>Although for common uses the <b>gamma</b> value just controls the subjective brightness of the mid range
of pixels, there are certain situations in a photo stitching workflow where it makes a quantitative difference
to the results:
</p>
<ul>
<li> Pixel values are interpolated when correcting TCA (transverse <a href="Chromatic_aberration.html" title="Chromatic aberration">chromatic aberration</a>).
</li>
<li> Pixel intensity is scaled when correcting <a href="Vignetting.html" title="Vignetting">vignetting</a>.
</li>
<li> Pixel values are interpolated when photos are re-projected into the output image.
</li>
<li> Blending via feathering, <a href="Enblend.html" title="Enblend">enblend</a> or smartblend<a class="external" href="http://wiki.panotools.org/Smartblend">[*]</a> averages pixel values between images.
</li>
</ul>
<p>In any of these situations, it may be necessary to work with linear data (gamma = 1.0) or to use tools that
work internally with gamma corrected data like so:
</p><p>When using <a href="Fulla.html" title="Fulla">fulla</a> to correct chromatic aberration and vignetting, be sure to set the <b>-i</b> parameter to
the gamma of your input images.
</p><p><a href="Nona.html" title="Nona">nona</a>, <a href="PTStitcher.html" title="PTStitcher">PTStitcher</a> and <a href="PTmender.html" title="PTmender">PTmender</a> all accept a <b>g</b> (gamma) parameter on the <b>m</b> line, most
GUI front-ends<a class="external" href="http://wiki.panotools.org/GUI_front-ends">[*]</a> allow you to set this.
</p><p><a href="Enblend.html" title="Enblend">enblend</a> (including version 3.0) appears to assume that input data is already gamma-corrected, so if you are
working with linear data you probably need to change to gamma = 2.2 before running enblend.
</p><p>See Helmut Dersch's article on <a rel="nofollow" class="external text" href="http://www.panotools.org/dersch/gamma/gamma.html">Interpolation and Gamma Correction</a>.
</p><p>For details see the w:gamma correction<a class="external" href="http://www.wikipedia.org/wiki/gamma_correction">[*]</a> article and the
<a rel="nofollow" class="external text" href="http://www.poynton.com/notes/colour_and_gamma/GammaFAQ.html">Gamma FAQ</a>.
</p>



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